Most trailer or caravan suspensions incorporate leaf springs, the usual leaf spring arrangement utilising a beam axle extending between two ground-engaging wheels, the beam axle being bolted to the centre of each of the two leaf springs, each leaf spring being normally mounted to the trailer or caravan chassis at one end by means of a fixed bracket and at the other end to a shackle. The fixed bracket provides an anchor point whilst the shackle allows the spring to lengthen or shorten according to the loads applied.
Whilst this type of beam axle suspension has proved satisfactory, there are a number of problems associated with it during use. One of these arises when a large degree of spring deflection takes place, this causing the centre of the spring to move in a longitudinal direction with respect to the direction of travel. Whilst in many instances this is not of great importance, provided the two springs are deflected simultaneously by approximately the same amount, sometimes, however, one spring is deflected more than the other, particularly when the springs are unevenly loaded, and the combined effect of flattening the spring and pivoting it about its mounting at one end causes only that wheel supported by that spring to move in a longitudinal direction with respect to the trailer, thus causing the axle to slew, the end result being that the trailer is caused to move in a direction which deviates from its previous straight line movement. Another commonly encountered problem with beam axle suspensions is that caused by the deflection of the springs during body roll of a caravan for example (under the influence of lateral forces), this resulting in a spring wind-up situation. This of course can cause the trailing vehicle to swerve dangerously and in turn cause the towing vehicle to "snake" or sway.
Furthermore, conventional beam-axle suspension systems undergo undesirable ride characteristics under the influence of varying loads, this mainly being due to the fact that the rate of a conventional suspension leaf spring is substantially constant regardless of the load or forces applied during use.
One attempt to overcome some of the above problems and which is known to the Applicant, utilises a pair of conventional shock absorbers, one on each side of the chassis, and each mounted having one end connected to and medially of the length of its corresponding spring and its other end to the underside of the chassis, and in an approximate vertical disposition. This arrangement has not proven to be satisfactory.
One of the main objects of this invention therefore is to provide an improved trailer suspension system which will greatly improve the ride and handling of the trailer during towing.
It is a further object of this invention to provide an improved trailer suspension which is of simple design, of low cost and which can be readily adapted to conventional leaf spring suspension systems.